This invention relates to the rearrangement of cycloorganopolysilazanes to cycloorganotrisilazanes. More specifically, this invention relates to preparation of cycloorganotrisilazanes using quaternary ammonium halides as a catalyst.
Silane blocking agents are used to replace active hydrogens with silyl groups. Replacement of active hydrogen with silyl groups often affords products which are more chemically stable and which undergo subsequent chemical reaction at sites other than the silyl blocked site. Hydrolysis of the silyl blocked site will subsequently regenerate the unprotected active hydrogen functionality. Difunctional silane blocking agents are available to selectively block primary amines, vic-diols and other difunctional sites, typically yielding 5-, 6-, and 7-member silicon-containing rings which are very stable to hydrolysis, oxidation and reduction. This process is termed cyclosilylation.
A useful technique for cyclosilylation is reaction with hexamethylcyclotrisilazane which forms stable blocked derivatives without formation of polymeric by-products and without need for bulky groups to be present on the substrate compound. This process has found wide use in the Pharmaceutical industry in the manufacture of such materials as steriods, salicylic, thiosalicylic, and anthranilic acids.
Cycloorganopolysilazanes may be prepared by the direct reaction of an organohalosilane with ammonia. Brewer, et al., J. Am. Chem. Soc., vol. 70, pg. 3888 (1948), discloses the preparation of cyclodimethylpolysilazanes from the reaction of dimethyldichlorosilane with ammonia. In the reaction of a diorganodihalosilane with ammonia, the reaction product is a mixture of cycloorganopolysilazanes. Many uses of cyclic silazanes prefer the cyclotrisilazane species.
Zhinkin, et al., U.S.S.R. SU. No. 368267, published Jan. 26, 1973, discloses a process for preparing hexamethylcyclotrisilazane via the catalytic rearrangement of octoamethylcyclotetrasilazane. The catalysts cited are ammonium sulfate, ammonium chloride, and sulfuric acid.
Arkles, et al., U.S. Pat. No. 4,557,039, issued Mar. 18, 1986, discloses a process for preparing cyclotrisilazanes by heating cyclotetrasilazanes in the presence of a Group VIII catalyst in the presence of hydrogen.